There are many applications where it is desirable to locate a signal and possibly to track it as it varies in frequency. Such applications range from relatively low frequencies, such as in power line monitoring where it is desired to find the power line frequency to a desired accuracy, to high frequencies as found in modern communication systems, such as modern mobile telephony systems (although in this context this is to be understood to encompass speech and/or data transmission).
The field of mobile telephony is an example of a system where signal power received at a receiver may vary significantly. The receiver may be a base station trying to communicate with a mobile device at the edge of the cell covered by the base station, and hence the received signal may be relativel y weak. Meanwhile a handset on another operator's network may be working on a similar frequency and be close to the base station such that its signal at the base station is relatively large. Such a signal can be referred to as a “blocker” or interferer, as it may degrade or inhibit what would otherwise be a viable reception of a desired signal. Similar problems may occur for devices trying to receive a signal from a base station and/or in a point to point communications system.
It is advantageous to be able to locate the frequency of the dominant signals and/or blockers. This may enable action to be taken to mitigate the effects of a blocker. For example, by estimating the interference that may occur due to the presence of a blocker and generating a signal to reduce or correct for that interference.